1. Field of the Invention
The present invention relates to a semiconductor device and to a method of manufacturing the same and, in particular, relates to a semiconductor device having memory cell portions and compensation capacitance portions on a single substrate and to a method of manufacturing the same.
2. Description of Related Art
As one of semiconductor devices, there is a DRAM (Dynamic Random Access Memory) having crown capacitors.
Since the shapes of lower and upper electrodes forming the crown capacitors are cubic, CVD (Chemical Vapor Deposition) excellent in step coverage is used for forming the electrodes.
However, the treatment temperature is relatively high (e.g. 550 to 650° C.) in the CVD. As a consequence, there is a possibility that, during the formation of the upper electrode, reactions are induced between the lower electrodes and a capacitance insulating film, which have already been formed, and between the capacitance insulating film and the upper electrode which is being formed. These reactions cause a problem that the insulation of the capacitance insulating film is degraded to cause an increase in leakage current. In view of this, the formation of the upper electrode is carried out only for a minimum required time. Therefore, the upper electrode is thin and thus cannot fill up portions around the crown capacitors. As a result, spaces remain around (on the inner and outer peripheral sides of) the capacitors. These spaces should be filled up for the purpose of ensuring the mechanical strength and so on.
In a related semiconductor device, polysilicon is used for filling up spaces around crown capacitors (see, e.g. Patent Document 1: JP-A-2010-226022).
On the other hand, there is also known a semiconductor device using, as a capacitance plate electrode, silicon germanium (SiGe) containing a p-type impurity (e.g. boron) (see, e.g. Patent Document 2: JP-A-2003-224204).
The present inventor has recognized the following respects.
In the related semiconductor device, as described above, polysilicon is used for filling up the spaces around the crown capacitors. This polysilicon is made conductive so as to form a capacitance plate electrode. However, in order to make polysilicon conductive, a heat treatment of at least 600° C. is required for sufficiently activating an impurity introduced into the polysilicon. There is a possibility that such a high-temperature heat treatment promotes a reaction between an upper electrode and a capacitance insulating film to degrade the insulation of the capacitance insulating film more than the case where the upper electrode is formed by CVD.
On the other hand, silicon germanium containing a p-type impurity can be formed (made conductive) at a lower temperature as compared with polysilicon. However, there is a problem that its thickness should be made large in order to ensure the conductivity required for a semiconductor device.